Revised NaI Detector Shielding

Moving on from the last shield configuration (Shield 5), quite a bit more lead was obtained with the help of Hannah. In particular, shielding by the PMTs were significantly increased. More sheets hanging over the rack was also added.

Shield 6
Figure 1: Interior of shield	Figure 2: Interior of shield	Figure 3: Exterior of shield
Figure 4: Exterior of shield	Figure 5: Exterior of shield	Figure 6: Exterior of shield
Poly shown in Figure 6 composes the collimator to house the Cf-252 source.

Figure 7: Comparing shield 5 and background

Figure 8: Comparing shield 6 and shield 5

In Figure 7, only the peak amplitudes should be compared. A different discriminator with lower thresholds was used for the Shield 5 and Shield 6 run. Higher thresholds were used for the “Background” run due to the availability of equipment.

No appreciable difference can be seen between Shield 5 and the the revamped shield (Shield 6). This is despite there being roughly double the lead on the sides and much more lead surrounding the PMTs. I am not sure why no improvements were observed. Where should we go from here?

What would sources of the coincident background be? Coincidence plots for the Shield 6 run are shown in Figures 9 and 10.

Figure 9: Shield 6 Coincidence Plot	Figure 10: Shield 6 Coincidence Log Plot